Field of the Invention
The present invention relates to an image generating device and an image generating method.
Description of the Related Art
Examination of fundus is widely performed for early diagnosis of illnesses that are leading causes of lifestyle related diseases and blindness. For example, there is a scanning laser ophthalmoscope (SLO) that is an ophthalmic device using the principle of a confocal laser scanning microscope. The SLO is a device that performs raster scan of a fundus with a laser, which is measuring light, to obtain a planar image from the intensity of the return light, at high resolution and high speed.
In recent years, an adaptive optics SLO (AO-SLO) including an adaptive optics system is developed, in which a wavefront sensor measures the aberration of an examined eye in real time, and a wavefront correction device corrects the aberration of the measuring light or the return light generated in the examined eye. A planar image with a high horizontal resolution (hereinafter, may be called AO-SLO image) can be acquired.
When a planar image with a high horizontal resolution is acquired, the imaging range to be photographed at a time, i.e., field angle, is narrowed down due to a problem of optical aberration of the device or an increase in the imaging time. Therefore, the fundus needs to be imaged at a plurality of positions in a relatively wide range to obtain information necessary for diagnosis and examination. In some cases, a local region of an eye of the subject is imaged for a plurality of times in a predetermined range to figure out the entire eye, even if the images are not high-magnification images.
However, in these cases, the relationship between the plurality of obtained photographed images needs to be figured out even if the area necessary for diagnosis and examination is imaged. More specifically, the positional relationship between the plurality of photographed images needs to be clarified to stitch the images according to the positions of the images to thereby generate one high-definition panoramic image.
To solve the problem, Japanese Patent Application Laid-open No. 2010-259543 proposes a combined device with a combination of an SLO device with a wide field angle and a high-resolution SLO device with a small field angle, thereby making an attempt to solve the problem. When a desired position of an examined eye is imaged, a fixation lamp for fixating the examined eye is often used. In an invention disclosed in Japanese Patent Application Laid-Open No. 2013-169332, the displayed position of the fixation lamp is adjusted according to the diopter scale of the examined eye to acquire a planar image of a desired position of the fundus.
Performing position adjustment of a plurality of images to create a panorama is a general method. However, when the characters of a high-definition image of fundus with a small field angle are significantly small structural objects, such as photoreceptor cells and capillary vessels, the characters may not be resolved in a wide-angle image. In this case, combining of a small-angle image with few characters and a wide-angle image is not easy, and there is a case in which the images do not match in the method disclosed in Japanese Patent Application Laid-Open No. 2010-259543. Even between small-angle images, when position adjustment of an image with few characters is performed first, there may be a case in which an image for which the position adjustment will be performed next does not match. Unmatched images tend to be prominent when there is a disorder in the eye to be observed, such as when the signal intensity is weak due to cataract or when a normal anatomical structure disappears due to other diseases.
Because of the problems, a plurality of small field angles needs to be imaged to include an overlapped area (overlap), in which both images include at least character points that are some kind of structural objects. For example, a region of fundus to be observed is sequentially imaged in a tile shape or according to the shape of a structural object, such as a blood vessel and a lesion (edema or bleeding) that serves as a character. However, even a little involuntary eye movement moves the examined eye, and the expected location is shifted. An image without an area overlapping with the images taken so far or an image without a character point in the previous image may be taken. In this case, if images with a small field angle are sequentially stitched in the order of imaging, an image in which the position cannot be determined may be generated depending on the order of stitching.
A false detection of the position adjustment can be suppressed if the imaging position can be recognized from imaging conditions. However, when a fixation index is used to adjust the imaging position as disclosed in Japanese Patent Application Laid-Open No. 2013-169332, there is usually involuntary eye movement of the examined eye, and particularly, it is significantly difficult to accurately specify the imaging position when the visual fixation of the affected eye is poor or when the tested person or animal cannot see the fixation lamp.